Lithium is often present in naturally occurring brines, but is only one of many ions present in the brine. Thus, to recover the lithium, it is often necessary to remove other ions in the brine in order to recover lithium as lithium salts that are sufficiently pure that they can be used in industrial or pharmaceutical applications. For example, cations such as magnesium, sodium, calcium, and potassium may be present with many counteranions such as chloride, bromide, sulfates, nitrates, borates, and the like. Some examples of natural brines that contain lithium are set forth in the following Table:
TABLE 1NATURAL BRINE COMPOSITIONGreatSaltonSilverDeadSaltBonnevilleSeaPeakSalar deSeaLakeBrineBrineBrineAtacamaOceanIsraelUtahUtahCalif.NevadaBrines ChileNa1.053.07.09.45.716.27.175.70K0.0380.6.040.61.420.81.851.71Mg0.1234.00.80.40.0280.020.961.37Li0.00010.0020.0060.0070.0220.020.150.193Ca0.040.051.50.50.00.711.460.043Cl1.916.014.016.015.0610.0616.0417.07Br0.00650.40.00.00.00.0020.0050.005B0.00040.0030.0070.0070.0390.0050.040.04Li/Mg0.00080.00050.00750.01750.7861.00.1560.141Li/K0.00260.00330.0150.00490.01550.0160.0810.113Li/Ca0.00250.00640.20.05830.00081.04.840.244Li/B0.250.66660.8571.00.0514.03.754.83(All values except ratios in weight percent)
Each ion that is present in addition to the lithium can be considered as an impurity for purposes of lithium extraction, as each presents its own problems when present in the recovered lithium or lithium salts.
For example, sodium shortens the useful life of lithium ion batteries. For pharmaceutical use, lithium carbonate should be of extreme purity and should not contain any other ions to the extent possible.
Magnesium impurity is problematic because it is accepted, although not proven, that lithium chloride crystal containing 0.07 wt % Mg may be too high in magnesium to be used for producing lithium metal and for subsequent use in the production of lithium organometallic compounds. Thus, the industry demands that organolithium catalysts in polymerization reactions be low in magnesium. Additionally, magnesium impurities can adversely effect the operation of a lithium electrolysis cell when producing lithium metal from lithium salts.
Thus, it is desirable to remove magnesium, in particular, and as many other ions as possible while processing the brine prior to recovering the lithium in the form of the desired salt.
For example, in U.S. Pat. No. 5,219,550 Brown and Boryta describe a method for producing chemical grade lithium carbonate from natural lithium containing brine by, inter alia, removing magnesium by solar concentration, wherein any remaining magnesium is removed by adding a base to precipitate magnesium as its carbonate and/or hydroxide salts.
U.S. Pat. No. 4,980,136 discloses a procedure for preparing chemical grade and low sodium lithium chloride that is substantially purified from boron and magnesium (battery grade, less than 20 ppm sodium and less than 5 ppm magnesium) from concentrated natural brine by crystallizing lithium chloride from a magnesium/lithium chloride brine to produce a chemical grade of lithium chloride crystal, followed by alcoholic extraction of the soluble lithium chloride from the crystal leaving sodium chloride as the insoluble phase. The alcohol solution containing the lithium chloride is then filtered and evaporated to form a high purity grade of lithium chloride crystal.
Another process for producing lithium chloride is set forth in Chilean Patent Application No. 550-95, which describes a procedure whereby a purified brine containing essentially lithium chloride is directly produced from natural brines that have been concentrated by solar evaporation and treated by an extraction process to remove boron. However, the sodium, magnesium, calcium, and sulfate levels in the resultant brine are too high to be an acceptable brine source of lithium chloride for producing a technical grade lithium metal, primarily because the two major remaining impurities, sodium and magnesium, have to be further reduced to acceptable levels to produce chemical grade lithium chloride crystal. Specifically, magnesium must be reduced to less than 0.005 wt % Mg, and sodium to less than 0.16 wt % Na in the anhydrous lithium chloride salt. Salting out anhydrous lithium chloride directly from brine above 110° C. in a vacuum crystallizer as described in U.S. Pat. No. 4,980,136 yields a lithium chloride containing at best 0.07 wt % Mg and 0.17 wt % Na.
One such commercial method involves extraction of lithium from a lithium containing ore or brine to make a pure lithium sulfate solution such as described in U.S. Pat. No. 2,516,109, or a lithium chloride solution such as described in U.S. Pat. No. 5,219,550. After purifying the solutions, sodium carbonate is added as either a solid or a solution to precipitate lithium carbonate crystals. The lithium carbonate is subsequently filtered from the spent liquor (mother liquor), and the lithium carbonate is washed, dried, and packaged.
Lithium carbonate is often used as a feed material for producing other lithium compounds such as lithium chloride, lithium hydroxide monohydrate, lithium bromide, lithium nitrate, lithium sulfate, lithium niobate, etc. Lithium carbonate itself is used as an additive in the electrolytic production of aluminum to improve cell efficiency and as a source of lithium oxide in the making of glass, enamels, and ceramics. High purity lithium carbonate is used in medical applications.
For example, a presently used commercial procedure for producing chemical grade lithium chloride is to react a lithium base such as lithium carbonate or lithium hydroxide monohydrate with concentrated hydrochloric acid to produce a pure lithium chloride brine. The resultant lithium chloride brine is evaporated in a vacuum crystallizer at or above 110° C. to produce an anhydrous lithium chloride crystal product. This procedure yields a product that meets most commercial specifications for chemical grade lithium chloride, but not low sodium grades of lithium chloride. Chemical grade lithium chloride is suitable for air drying applications, fluxes, an intermediate in manufacture of mixed ion-exchange zeolites, and as a feed to an electrolysis cell for producing chemical grade lithium metal. Chemical grade lithium metal is used, inter alia, to produce lithium organometallic compounds. These compounds are used as catalysts in the polymerization and pharmaceutical industries.
Chemical grade anhydrous lithium chloride should contain less than 0.16% sodium in order to produce metal containing less than 1% sodium. The importance of minimizing the sodium content in the metal and the costs associated therewith are the principal reasons for using lithium hydroxide monohydrate or lithium carbonate as the raw material for producing lithium chloride and, subsequently, lithium metal. In consideration, low sodium lithium chloride, typically contains less than 0.0008 wt % sodium, and is commercially produced to manufacture low sodium lithium metal suitable for battery applications and for producing alloys.
Commercially, low sodium lithium chloride is produced indirectly from chemical grade lithium carbonate. Chemical grade lithium carbonate is produced from Silver Peak Nevada brine, Salar de Atacama brines in Chile, Hombre Muerto brines in Argentina, and from spodumene ore (mined in North Carolina). The lithium carbonate is converted to lithium hydroxide monohydrate by reaction with slaked lime. The resultant slurry contains precipitated calcium carbonate and a 2-4 wt % lithium hydroxide solution, which are separated by filtration.
The lithium hydroxide solution is concentrated in a vacuum evaporation crystallizer in which the lithium hydroxide monohydrate is crystallized, leaving the soluble sodium in the mother liquor solution. The crystalline lithium hydroxide monohydrate is separated from the mother liquor, washed, and dried. This salt normally contains between 0.02 and 0.04% sodium. To further reduce the sodium levels, the lithium hydroxide monohydrate must be dissolved in pure water and recrystallized, and subsequently reacted with pure hydrochloric acid to form a concentrated lithium chloride brine containing less than 10 ppm sodium. The resultant lithium chloride solution is then evaporated to dryness to yield anhydrous lithium chloride suitable for producing battery grade lithium metal containing less than 100 ppm sodium. The above process requires seven major processing steps described as follows:
1) Extraction and purification of a low boron aqueous solution containing 0.66 to 6 wt % Li from lithium containing ore or natural brine;
2) Purification of the brine with respect to magnesium and calcium and filtration;
3) Precipitation of lithium carbonate from the purified brine by addition of Na2CO3, and filtering and drying the lithium carbonate;
4) Reacting slaked lime and lithium carbonate to produce a LiOH solution and filtering to remove calcium carbonate;
5) Crystallizing LiOH.H2O in a vacuum crystallizer,
6) Dissolving the LiOH.H2O crystals and re-crystallizing LiOH.H2O from solution; and
7) Reacting high purity HCl with re-crystallized LiOH.H2O to produce a high purity lithium chloride brine from which low sodium lithium chloride is crystallized and drying the lithium chloride.
Low sodium lithium carbonate can be prepared from re-crystallized LiOH.H2O using the first part of the process described above. The recrystallized LiOH.H2O is then mixed with water and reacted with CO2 to precipitate the lithium carbonate. The processing steps are set forth below:
1) Extract and purify a low boron aqueous solution containing 0.66 to 6 wt % Li from lithium containing ore or natural brine;
2) Purify the brine with respect to magnesium and calcium and filtration.
3) Precipitate Li2CO3 from the purified brine with the addition of Na2CO3, filtration, and drying.
4) React slaked lime and Li2CO3 to produce a LiOH solution and filter.
5) Crystallize LiOH.H2O in a vacuum crystallizer.
6) Dissolve again and re-crystallize LiOH.H2O from solution.
7) React CO2 gas with a slurry containing re-crystallized LiOH.H2O to crystallize low sodium high purity lithium carbonate crystal, filter, and dry.
Production of lithium chloride directly from concentrated brine has also been described in U.S. Pat. No. 4,274,834.
In prior patents methods of recovering highly purified lithium salts, e.g., lithium carbonate and lithium chloride, from salt brines were described. (See. e.g., U.S. Pat. No. 6,207,126. This and all patents and references cited herein are incorporated herein by reference in their respective entireties for all purposes.) A very basic overview of the processes described therein is that ionic impurities from the brine must be removed in order to recover lithium salts of sufficiently pure levels for use in a given application, e.g., lithium ion batteries, pharmaceutical applications, etc. Purification takes place by removing calcium, boron, magnesium, and other naturally occurring impurities by, e.g., precipitating those impurities as salts which are insoluble under the conditions present in the brine. It is particularly important to remove magnesium from the brine, and presently this is removed by precipitating magnesium as carnallite (KMgCl3.6H2O) and, once potassium levels are sufficiently reduced, as bischofite (MgCl2.6H2O). During this process, the lithium concentration in the brine gradually increases to a level such that it begins to precipitate along with the magnesium as lithium carnallite (LiMgCl3.7H2O). This continues until the brine contains about 6% Li and about 2% Mg. Extremely pure lithium salts are then produced from this brine. A difficulty with this process presents in the loss of lithium during lithium carnallite precipitation.
New processes of removing magnesium from lithium containing brines without loss of lithium are required.